The invention relates to a method for manufacturing workpieces with small corner radii in relation to the thickness to be cut, and greatly reduced edge reduction in a fine blanking tool of a fine blanking machine, wherein the workpiece is clamped between two tool parts respectively consisting of an upper and a lower cutting die, as well as of an upper and a lower cutting punch, and the cutting is realized by the combined efforts of upper and lower cutting punches.
The invention further relates to a tool for fine blanking of workpieces with small corner radii in relation to the thickness to be cut, and greatly reduced edge reduction, from a cutting strip, a sheet, a coil material or the like, with two clamping the latter tool halves respectively consisting of at least one cutting die and one cutting punch.
The limitations of fine blanking of portions with small corner radii in relation to the thickness of the sheet to be cut and to the quality of the material are sufficiently known. Based on experience, a fine blanking severity is defined which distinguishes the severity degrees Si (easy), S2 (medium) and S3 (difficult) (see “Umformen and Feinschneiden”, in Handbuch fur Verfahren, Werkstoffe, Teilegestaltung, pages 154 to 165, Verlag Hallwag AG, 1997, Switzerland). Thus, the severity degree is essentially defined by the cutting path geometry and the thickness of the metal sheet. For this, the cutting path geometry is divided into simple geometric basic areas such as corner radii, hole diameters, groove and fin widths. From the ratio between a geometric dimension and the thickness of the metal sheet, the severity degree of fine blanking is defined, which grows with growing metal sheet thickness. That means that fine blanking of large-area thin parts is easier than fine blanking of narrow fins or rings with greater sheet thickness. Also, obtuse-angled corners with big radii are to be cut better than sharp-cornered structure with small radii.
A method is known from DE 39 31 320 C1 for manufacturing burr-free workpieces by punch counter cutting, for example, in an fine blanking tool, wherein a cutting strip from which the workpiece is to be cut is clamped between two tool parts, respectively consisting of an upper and a lower cutting die as well as of an upper and a lower cutting punch, and the cutting is realized by the combined efforts of upper and lower cutting punches, wherein cutting of the workpiece is started along a cutting line and then the workpiece is cut out in the opposite direction.
This state of the art exactly shows the intended reduction on both sides as a result of counter cutting.
Typical characteristics of fine blanking parts are edge reduction and burr. Especially at corner portions, edge reduction occurs, which grows with corner radii becoming smaller and with increasing sheet thickness. The reduction depth may be about 20% and the reduction width may be 30% of the sheet thickness or more (see DIN 3345, Feinschneiden; August 1980). Thus, this reduction depends on the thickness and quality of the material, so that controlling it is possible only in a limited way, and often results in limited functioning of parts, for example, because of lack of sharp-edged tips of interlocking parts or because of the changes in the functional length of parts.
At this state of the art, it is an object of the invention to improve a method and a tool for manufacturing workpieces in such a way that fine blanking can be also applied for parts with small corner radii and sharp-edged corners with greater sheet thickness, without limiting the function of the parts and at the same time providing economic advantages.